Control system for coating continuous webs

ABSTRACT

Described is a system for controlling the amount of coating per unit of area applied to a continuous web which passes through a dip tank and thence through squeeze rolls and one or more drying chambers. The system also incorporates means for controlling tension in a dried web, which tension is a function of the amount of coating applied per unit of area. The foregoing is accomplished by controlling the amount of concentrated coating solution fed to a blending tank, which supplies the dip tank, as a function of web speed; by controlling the pressure exerted on the web by the squeeze rolls as a function of the liquid level in the blending tank to which excess solution from the squeeze rolls and dewatering pads is fed; and by controlling the amount of solvent for the concentrated coating solution fed to the blending tank as a function of the tension in the dried web. The invention additionally includes means for directly monitoring the density of the coating solution in the blending tank and for adjusting that density should it depart from a predetermined set value.

United States Patent James T. Carleton;

1 ST DRYER I [72] lnventors Richard E. Putman, both of Pittsburgh, Pa.

[21] Appl. No. 887,499 [22] Filed Dec. 23, 1969 [45] Patented Aug. 17, 1971 [73] Assignee Westinghouse Electric Corporation Pittsburgh, Pa.

[54] CONTROL SYSTEM FOR COATING CONTINUOUS WEBS 9 Claims, 1 Drawing Fig.

[52] US. Cl 118/8, 118/33,118/419 [51] lnt.Cl .B05c 11/10 [50] Field of Search 118/6, 7, 8;

[56] References Cited UNITED STATES PATENTS 2,942,352 6/1960 Eicken-Estienne.. 1 18/6 UX 2,981,638 4/1961 Jones 118/6 X 3,251,710 5/1966 ll8/7X 3,292,573 12/1966 1 18/7 ekeo 3,319,637 5/1967 GoreetaL...

118/7 X 3,425,861 2/1969 Jones 118/7 X 3,515,094 6/1970 McVey 1 18/7 X Primary Examiner-Morris Kaplan Attorneys-F. l-l. Henson and R. G. Brodahl ABSTRACT: Described is a system for controlling the amount of coating per unit of area applied to a-continuous web which passes through a dip tank and thence through squeeze rolls and one or more drying chambers. The system also incorporates means for controlling tension in a dried web, which tension is a function of the amount of coating applied per unit of area. The foregoing is accomplished by controlling the amount of concentrated coating solution fed to a blending tank, which supplies the dip tank, as a function of web speed; by controlling the pressure exertedon the web by the squeeze rolls as a function of the liquid level in the blending tank to which excess solution from the squeeze rolls and dewatering pads is fed; and by controlling the amount of solvent for the concentrated coating solution fed to the blending tank as a function of the tension in the dried web. The invention additionally includes means for directly monitoring the density of the coating solution in the blending tank and for adjusting that density should it depart from a predetermined set value.

TENSION MEASUREMENT DEWATERING PADS CONCENTRATED COATING SOLUTION SEPARATOR 7a 100 LEVEL CONTROL as, DENSITY CONTROLLER 5 LG? SOLVENT PATENTED AUG] 719m at g om. Q.

CONTROL SYSTEM FOR COATING CONTINUOUS WEBS BACKGROUND OF THE INVENTION in the coating of continuous webs, particularly absorbent webs, the web material is initially passed through a dip tank which applies the coating solution to the web, then through squeeze rolls and dewatering pads which remove excess coating solution from the web, and finally through drying chambers where a solvent, such as water, is evaporated. Normally the dip tank is supplied by a blending tank where concentrated coating solution,of density greater than the desired density, is diluted with a solvent and to which excess coating material from the squeeze rolls and dewatering pads is returned.

in such a system, the amount of coating per square unit of area leaving with the web and the amount of liquid leaving with the web will be known if a desired and known amount of coating solution of known density is fed to the system at a predetermined ratio to web speed, and if a material balance is achieved. Thus, maintenance of a predetermined liquid level in the blending tank (indicative of a material balance wherein the amount of concentrated solution, solvent and return from the squeeze rolls and dewatering pads is equal to the amount of solution deposited on the web) and coating solution density are major parameters in controlling a coating system of the type described. if either one or both of these should vary, corrective action must be taken to obtain the desired quality in the finished material.

- SUMMARY OF THE lNVENTlON As an overall object, the present invention seeks to provide new and improved apparatus for controlling a coating line for continuous webs, particularly webs formed from previous or absorbent material, wherein the amount of coating per square unit of area and the density of the coating as applied to the web can be accurately controlled.

Another object of the invention is to provide a system ofthe type described for accurately controlling the amount of coating per unit of area applied to a web surface and a system for direct measurement of the amount of water or solvent applied to, the material. I

Still another object of the invention is to provide a system for regulating a web-coating plant to hold tension constant, assuming that the temperature profile and stretch of the web are automatically held constant by other means.

in accordance with the invention, a coating line is provided wherein a web passes through a coating. solution in a'dip tank and thence through squeeze rolls and dewatering pads where excess coating solution is removed from the web. This excess coating is returned to a blending tank which supplies coating solution to the dip tank. First means, either a valve or pump, is provided for feeding concentrated coating solution to the blending tank. Second means, also a pump or valve, is provided for feeding a solvent to the blending tank where it is mixed with the concentrated coating solution. A device, such as a tachometer, measures the speed of a web and controls the flow of concentrated coating solution to the blending tank as a function of the thus measured speed. In this manner, as the speed of the web increases, so also will the amount of concentrated coating solution which is fed to the blending tank.

The system additionally includes means for determining the density of the coating solution in the blending tank and for controlling the rate of How of solvent to the blending tank as a function of the measured density. This means may comprise apparatus for measuring the tension in the web after it has been dried, since variations in tension of the dried web are caused by changes in moisture present in the cloth when it enters the drying apparatus. This moisture content, in turn, is a function of the amount of solvent added to the blending tank. Measurement of density may also be accomplished directly by means of av density measuring device and corrective action taken to adjust the amount, of solvent added to the blending tank when. the density departs froma predetermined value.

As was mentioned above, the excess material removed from the web by the squeeze rolls and the dewatering pads is returned to the blending tank where the concentrated coating solution and solvent are mixed. In order to achieve a material balance where the amount of material leaving with the web is equal to the amount of concentrated coating solution and solvent added to the blending tank, the liquid level within the blending tank should be maintained constant. Means are provided for detecting a change in the level of the coating solution in the blending tank from a predetermined level; and if the level should change, apparatus is provided for controlling the pressure exerted by the squeeze rolls on the web such that a material balance will again be achieved.

The above and other objects and features of the invention will become apparent from the following detailed description taken in connection with the accompanying single figure drawing which schematically illustrates one embodiment of the invention.

With reference now to the drawing, a continuous web of material, identified by the reference numeral 10, passes between pull rolls 12 and thence into a dip tank 14 containing a coating solution 16. As an example, the web 10 may comprise tire cord and the coating solution 16 may comprise a liquid latex solution. The web 10 passes around a submerging roll 18 which forces it beneath the surface of the coating solution 16. After passing through the solution 16, the web 10 passes between squeeze rolls 20 which remove excess coating solution from the material. The pressure exerted by the squeeze rolls 20 may be regulated by means of a squeeze roll manipulator 22, hereinafter described ingreater detail. From the squeeze rolls 20, the web 10 passes through pull rolls 24 and then around roll 26 and rolls 28, 30 and 32. Connected to roll 30 is a tachometer generator 34 or the like which produces an output signal'on lead 36 which varies as a function ofthe speed ofthe web 10.

From roll 32, the web passes around roll 38 and then through first and second driers 40 and 42, respectively. From drier 42, the web 10 passes through a rollevator 44 where it passes around vertically movable upper rolls 46 and 48 and lower stationary rolls 50 and 52. The rolls 46 and 48 are connected through chains 54 and 56 to rolls 58 and 60 around which the web passes after passing around roll 62. Beneath the rolls 58 and 60 are rolls 64 and 66, the roll 66 being connected to a tension measurement device 68 which measures the tension in the web 10, which now is dried.

Beneath the dip tank 14 is a blending tank 70 to which concentrated coating solution is fed via conduit 72. Also fed into the bottom of the blending tank 70 via conduit is a solvent which, for example, may comprise water. Coating solution from the blending tank 70 is pumped into the dip tank 14 through pump 76 and conduit 78. The pump 76 operates continuously with the overflow from the dip tank 14 and any excess material removed by the squeeze rolls 20 being returned to the blending tank via conduit 74.

The coated web, after passing around roll 32, passes over dewatering pads 77 which are connected to a separator 79 connected to pump 80 which creates a partial vacuum within the separator 79 and in the area of the web above the dewatering pads 77. The excess liquid thus removed by the dewatering pads and passing through the separator 79 is returned to the blending tank through conduit 82.

A portion of the coating solution, which is continuously pumped by pump 76, is returned to the blending tank 70 through a density measuring device 84 which, for example, may comprise a weighted U-tube or other similar density measuring device. The device 84 produces an electrical signal on lead 86 proportional to density which is applied to a density controller 88. The density controller 88, in turn, controls a valve 90 in conduit 75 supplying solvent to the blending tank 70. Thus, the density of the coating solution within the blending tank 70 will be dependent upon the setting of valve 90 and the amount of solvent added to the concentrated coating solutron.

Provided in the conduit 72 is a pump 92 controlled by a pump control circuit 94. The pump control circuit 94, in turn, is controlled by the electrical signal on lead 36 produced by tachometer generator 34. As was explained above, the electrical signal produced by the tachometer generator is proportional to the speed of the web 10. Hence, the amount of concentrated coating solution supplied to the blending tank will always be proportional to the web speed.

Finally ,.departure of the level of the coating solution in the blending tank 70 from a predetermined, set level is detected by means of level detector 96 which, when the level departs from its predetermined set level, will produce an electrical signal on lead 98 to actuate level control circuit 100 to increase or decrease the pressure exerted by the squeeze rolls via squeeze roll manipulator 22. That is, if the level should increase, the pressure exerted by the squeeze rolls is decreased; and if the level should decrease, indicating that there is a reduction in material being returned by the squeeze rolls, the pressure exerted by the manipulator 22 is increased.

In operation, in order to start up the system, the dip tank 14 is lowered away from the web 10. Some water or other solvent is fed to the blending tank 70 by hand and the recirculation pump 76 started. The density controller 88 is then switched to automatic and concentrated coating solution fed by hand until the level in the tank is just below the desired controlled level, the density meanwhile being controlled at a specified value by automatic water addition. Circulation up to the dip tank 14 naturally takes place at this stage with overflow back to the blending tank 70 by virtue of the fact that pump 76 is operatmg.

The squeeze rolls 20 are then set by hand to a predetermined pressure. The trough or tank 14 is then raised and the pump control circuit 94 switched to automatic. Additional concentrated coating solution is now fed-to the blending tank 70 at a rate proportional to the speed of the web 10, while excess coating solution from the squeeze rolls 20 and the dewatering pads 77 flows back to the blending tank 70. The density of the coating solution will, however, tend to rise due to some water leaving the system with the web, combined with the feed of new concentrated coating solution via conduit 72. The density controller 88 will, therefore, respond and add more solvent via valve 90 to maintain the solution density at the desired value as determined by the density measuring device 84. The squeeze rolls 20 are now adjusted slightly by hand until the level in the blending tank 70 stops rising, whereupon the squeeze roll manipulator 22 is switched to automatic. Once equilibrium is reached, the level should not change. However, should the level change, this is sensed by the level detector 96 which, through level control circuit 100, adjusts the pressure exerted by the squeeze roll manipulator 22 until the amount of solution returned from the squeeze rolls again maintains the level within the blending tank 70 constant.

In a system such as that shown herein, where stretch and temperature profile through the plant are controlled, variations in tension in the dried web are caused by changes in moisture content in the cloth when it enters the driers. This moisture content, in turn, is a function of the density of the coating solution within the blending tank 70. Consequently, by measuring the tension in the dried web via tension measurement circuit 68, and by feeding a signal back to the density controller 88, the position of valve 90 and the amount of solvent fed to the blending tank 70 are controlled as a function of the tension in the dried web. The density of the solution within the blending tank 70 is, of course, also monitored directly by the density measuring device 84 as was explained above.

Although the invention has been shown in connection with a certain specific embodiment, it will be readily apparent to those skilled in the art that various changes in form and arrangement of parts may be made to suit requirements without departing from the spirit and scope of the invention. In .this

respect, it will be apparent that a further improvement in contro can be obtained by controlling the temperature of the coating solution within the blending tank 70.

We claim as our invention:

1. In a coating system for continuous webs and the like wherein the web passes through a coating solution in a dip tank and thence through squeeze rolls where excess coating solution is removed from the web by the squeeze rolls is returned to a blending tank which supplies coating solution to the dip tank; the combination of first means for feeding concentrated coating solution to said blending tank, second means for feeding a solvent to said blending tank where it is mixed with the concentrated coating solution, means for measuring the speed of said web and for controlling the flow of concentrated coating solution to said blending tank as a function of measured speed, means for determining the density of the coating solution in said blending tank and for controlling the rate of flow of solvent to the blending tank as a function of measured density, means for detecting a change in the level of the coating solution in said blending tank from a predetermined level, and apparatus responsive to said last-named means for controlling the pressure exerted by the squeeze rolls on said web.

2. The combination of claim 1 wherein the means for feeding concentrated coating solution to said blending tank comprises a pump and the means for controlling the flow of concentrated coating solution to the blending tank as a function of measured speed includes a tachometer generator connected to a roll over which the web passes, control circuitry for said pump, and means for applying an electrical signal from said tachometer generator proportional to the speed of said web to said control circuitry whereby said pump will be controlled as a function of the speed of said web.

3. The combination of claim 1 wherein said second means for feeding a solvent to said blending tank comprises a valve.

4. The combination of claim 1 wherein said means for determining the density of the coating solution in said blending tank and for controlling the rate of flow of solvent to the blending tank comprises a density measuring device through which coating solution in said blending tank is circulated, and means coupled to said density measuring device for controlling the flow ofsolvent to said blending tank.

5. The combination of claim 1 including means for drying said web after passage through said squeeze rolls, and wherein said means for determining the density of the coating solution in said blending tank and for controlling the rate of flow of solvent to the blending tank comprises means for measuring the tension in said web after it has been dried and for producing an electrical signal proportional to said measured tension, and means responsive to said electrical signal for controlling the rate of flow of solvent to said blending tank.

6. The combination of claim 1 including means for continuously circulating coating solution from said blending tank to said clip tank, the overflow from said dip tank being returned to the blending tank.

7. The combination of claim 1 including dewatering pads in the path of travel of said web beyond said squeeze rolls for removing excess liquid fromsaid web, and means for returning the excess liquid removed by said dewatering pads back to said blending tank.

8. The combination of claim 1 wherein the apparatus for controlling the pressure exerted by said squeeze rolls increases said pressure when the level in said blending tank falls and decreases said pressure when the level in said blending tank rises.

9. The combination of claim I including dewatering pads in the path of travel of said web, and means for returning the coating solution removed by said dewatering pads to said blending tank. 

1. In a coating system for continuous webs and the like wherein the web passes through a coating solution in a dip tank and thence through squeeze rolls where excess coating solution is removed from the web by the squeeze rolls is returned to a blending tank which supplies coating solution to the dip tank; the combination of first means for feeding concentrated coating solution to said blending tank, second means for feeding a solvent to said blending tank where it is mixed with the concentrated coating solution, means for measuring the speed of said web and for controlling the flow of concentrated coating solution to said blending tank as a function of measured speed, means for determining the density of the coating solution in said blending tank and for controlling the rate of flow of solvent to the blending tank as a function of measured density, means for detecting a change in the level of the coating solution in said blending tank from a predetermined level, and apparatus responsive to said last-named means for controlling the pressure exerted by the squeeze rolls on said web.
 2. The combination of claim 1 wherein the means for feeding concentrated coating solution to said blending tank comprises a pump and the means for controlling the flow of concentrated coating solution to the blending tank as a function of measured speed includes a tachometer generator connected to a roll over which the web passes, control circuitry for said pump, and means for applying an electrical signal from said tachometer generator proportional to the speed of said web to said control circuitry whereby said pump will be contRolled as a function of the speed of said web.
 3. The combination of claim 1 wherein said second means for feeding a solvent to said blending tank comprises a valve.
 4. The combination of claim 1 wherein said means for determining the density of the coating solution in said blending tank and for controlling the rate of flow of solvent to the blending tank comprises a density measuring device through which coating solution in said blending tank is circulated, and means coupled to said density measuring device for controlling the flow of solvent to said blending tank.
 5. The combination of claim 1 including means for drying said web after passage through said squeeze rolls, and wherein said means for determining the density of the coating solution in said blending tank and for controlling the rate of flow of solvent to the blending tank comprises means for measuring the tension in said web after it has been dried and for producing an electrical signal proportional to said measured tension, and means responsive to said electrical signal for controlling the rate of flow of solvent to said blending tank.
 6. The combination of claim 1 including means for continuously circulating coating solution from said blending tank to said dip tank, the overflow from said dip tank being returned to the blending tank.
 7. The combination of claim 1 including dewatering pads in the path of travel of said web beyond said squeeze rolls for removing excess liquid from said web, and means for returning the excess liquid removed by said dewatering pads back to said blending tank.
 8. The combination of claim 1 wherein the apparatus for controlling the pressure exerted by said squeeze rolls increases said pressure when the level in said blending tank falls and decreases said pressure when the level in said blending tank rises.
 9. The combination of claim 1 including dewatering pads in the path of travel of said web, and means for returning the coating solution removed by said dewatering pads to said blending tank. 